Solid state polymerization of polyesters in the presence of a diisocyanate

ABSTRACT

There is disclosed an improvement in the solid state polymerization of melt polymerized polyester resin to produce polyester resins having intrinsic viscosities of at least 1.0 as determined in a 60/40 phenol/tetrachloroethane mixed solvent at 30*C. comprising adding to said melt polymerized polyester resin, prior to the solid state polymerization thereof, from 0.1 to 2.0 percent by weight of an organic aromatic diisocyanate which diisocyanate material provides for increased solid state polymerization rates.

Uite tates atermt Sid-Ahmed et a1.

William C. Tung, Tallmadge, both of Ohio The Goodyear Tire & Rubber Company, Akron, Ohio Filed: May 1, 1974 Appl. No.2 465,984

Assignee:

U.S. Cl 260/75 NE, 260/775 SS Int. Cl C08g 22/10, C08g 22/26 Field of Search 260/75 NE, 77.5 SS

References Cited UNITED STATES PATENTS 2/1971 Rye et a1. 260/775 SS in 3,853,821 Dec. 10, 1974 5/1971 Stewart et al 260/77.5 SS 2/1972 Flint 260/77.5 SS

There is disclosed an improvement in the solid state polymerization of melt polymerized polyester resin to produce polyester resins having intrinsic viscosities of at least 1.0 as determined in a 60/40 phenol/tetrachloroethane mixed solvent at 30C. comprising adding to said melt polymerized polyester resin, prior to the solid state polymerization thereof, from 0.1 to 2.0 percent by weight of an organic aromatic diisocyanate which diisocyanate material provides for increased solid state polymerization rates.

ABSTRACT 5 Claims, No Drawings SOLID STATE POLYMERIZATION OF POLYESTERS IN THE PRESENCE OF A DIISOCYANATE This invention relates to the polymerization of linear polyester resins in the solid state. More particularly this invention relates to an improvement in the solid state polymerization whereby the polymerization can be carried out at accelerated rates.

In solid state polymerization processes designed to produce polyester resins having intrinsic viscosities of at least l.0, polyester resin, prepared by esterification or transesterification of-a dicarboxylic acid or C, to C alkyl ester thereof with a glycol and subsequent melt polymerization, is first reduced to a finely divided state and then heated in solid form under conditions which promote further condensation and allow for the removal of gaseous by-products. Generally these conditions involve heating the polyester resin in a suitable apparatus in a stream of an inert gas such as nitrogen or under conditions of high vacuum. However, the temperatures that can be used for the solid state polymerization are limited by the sticking temperature and the melting point of the polyester resin. For example, in the solid state polymerization of poly(ethylene terephthalate), the highest temperatures which can be employed range from 240 to 245 C., which temperatures are just below the sticking temperature of this polyester and about C. below its melting temperature. As a result the polymerization rate of poly(ethylene terephthalate) is slow, requiring several hours of treatment A ganic aromatic diisocyanates include diphenylme lll to achieve high molecular weight product, i.e., product having an intrinsic viscosity of. 1.0 or higher.

A means has now been found for accelerating the polymerization rate during the solid state polymerization of melt polymerized polyester resin, thus providing for significantly shorter than normal process times. According to the present invention accelerated solid state polymerization rates can be achieved, in the production of polyester resin having an intrinsic viscosity of at least 1.0, by incorporating in the melt polymerized polyester resin, prior to carrying out the solid state polymerization thereof, from 0.1 to 2.0 percent by weight of an organic aromatic diisocyanate corresponding to the formula O=C=NRN=C=O where R is a divalent aromatic radical selected from the group consisting of radicals of the formulae where R is selected from the group consisting of hydrogen atom and alkyl radicals containing from l to 10 carbon atoms, R" is selected from the group consisting of hydrogen atom, alkyl radicals containing from 1 to 10 carbon atoms and alkoxy radicals containing from 1 to 10 carbon atoms and Y is a direct bond or methylene radical, based on the weight of the melt polymerized polyester resin.

In the practice of the present invention any of the well known and commercially available organic aromatic diisocyanates, corresponding to the above formulae can be employed to accelerate the solid state polymerization rate. Representative examples of such orthane-4,4'-diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, bitolylene diisocyanate (diphenyl-3,3'-dimethyl-4,4-diisocyanate), dianisidine diisocyanate (diphenyl-3,3-dimethoxy-4,4'-diisocyanate), metaphenylene diisocyanate, paraphenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthylene di isocyanate and the like. Especially useful organic aromatic diisocyanates include dianisidine diisocyanate, bitolylene diisocyanate and diphenylmethane-4,4'- diisocyanate as exemplified in the illustrative examples herein.

As disclosed hereinabove, the organic aromatic diisocyanates useful in this invention are added to the melt polymerized polyester resins in amounts ranging from 0.1 to 2.0 percent by weight based on the weight of said polyester resins and at a point in time prior to carrying out the solid state polymerization thereof. In general the aromatic diisocyanate is incorporated into the melt polymerized polyester resin at the beginning, during or after completion of the polycondensation stage of either the esterification-polycondensation or transesterification-polycondensation polyester forming processes described above. It is most convenient, however, to in corporate the aromatic diisocyanate into the melt poly merized polyester resin at the beginning of the polycondensation stage of the polyester forming process.

The term melt polymerized polyester resin as used throughout this specification means linear polyesters and copolyesters prepared by any of the well known polyester forming processes known in the art wherein melt polymerization constitutes one stage in the process. Thus the melt polymerized polyester resins to which the present invention is applicable include those linear polyester and copolyester resins prepared by either the direct esterification-polycondensation process wherein a dicarboxylic acid and a diol of the series HO(CH OH, where n is an integer ranging from 2 to 10, are first reacted together to form a diglycol ester which is then polycondensed under melt conditions to high molecular weight product or the transesterification-polycondensation process wherein a C to C alkyl ester of a dicarboxylic acid and a glycol such as defined above are first reacted together to form a diglycol ester which is then subjected to melt polycondensation conditions .to form high molecular weight product. The reaction conditions of temperature, pressure, catalyst, etc. involved in carrying out the esterification or transesterification and polycondensation stages in these processes are all well known (see, for example, US. Pat. No. 3,756,866). I 7

Representative examples of dicarboxylic acids and C to C lower alkyl esters thereof which can be advantageously employed in these processes include terephthalic acid, isophthalic acid, diphenyl-p,p'-dicarboxylic acid, naphthalene dicarboxylic acids and the like and the dimethyl, diethyl, dipropyl and dibutyl esters thereof. Useful glycols corresponding to the above formula include ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, decamethylene glycol and the like. Also, glycols such as l,4-dimethanol cyclohexane have been found to be useful.

The present invention is also applicable to polyesters prepared from various combinations of two or more of the above described acids. esters and glycols. The preferred melt polymerized polyesters to which the present invention is applicable,however,are those in which The invention is illustrated below employing the at least 80 percent of the acid component consists of poly(ethylene terephthalate) samples prepared in acunits of terephthalic acid and at least 80 percent of the cordance with the above described procedure. All parts glycol component consists of units of ethylene glycol. and percentages are by weight unless otherwise indi- Five samples of melt polymerized poly(ethylene tere- 5 cated. The term l.V. as employed throughout the exphthalate) resin were prepared for subsequent use in amples represents the intrinsic viscosity of the polyes- Examples 1 5 hereinbelow. The five samples were ter sample as determined in a 60/40 phenolprepared by a transesterification-polycondensation tetrachloroethane mixed solvent at 30 C. The term process employing three-neck glass reaction tubes ap- COOH" represents the free carboxyl end group conproximately inches long and 1.75 inches in diame- 1Q centration of the polyester sample as determined by the ter. In each instance 70 grams of dimethyl terephthalmethod y POhl in Analytical Chemistry, 26, P g ate and 45 milliliters of ethylene glycol were added to 1614 and is expressed in equivalents P million the glass reaction tube which was submerged in a digrams of Polyester i g-lmethyl phthalate constant temperature bath. The reaction mixture was heated to l60- 165C. under a nitrol5 EXAMPLE 1 (Control) gen purge, after which 0.0236 gram of manganese ace- Fifteen grams of the ground pelylethylene {eretate was added. The reaction temperature was then inphthalate) prepared as describ ed hereinabove and concreased to 225 C. and the reaction allowed to proceed, taining no diisocyanate were polymerized in a cylindriwith constant agitation, until 29 milliliters of methanol cal glass reaction tube in the solid state employing fluby-product were collected. At this time 0.7 milliliter of idized bed techniques at a temperature of 245 C. The a triphenyl phosphite solution was added to the reacfluidizing media consisted of preheated nitrogen gas tion tube. The triphenyl phosphite solution was preflowing through the tube and polyester at a rate of pared by diluting four grams of triphenyl phosphite cubiccentimeters/minute. The table below conwith toluene to a total volume of 100 milliliters. The retains all pertinent data on the solid state polymerization action mixture was stirred for five minutes, after which :rate for this control experiment as evidenced by the in- 0.0l76 gram of antimony trioxide was added. The reac creases in the intrinsic viscosity (l.V.) of the samples tion temperature was gradually increased to 270 C. with time.

T f TABLE I Polymerization Time Minutes 0 15 45 60 75 90 105 1.v. 0.64 0.76 0.90 1.01 1.12 1.13 1.18 1.20 COOH 2s 23 17 16 17 and the pressure reduced, In four of the poly(ethylene terephthalate) preparations, after 21 milliliters of by EXAMPLES 2 product ethylene glycol were collected, the vacuum Flfteen grams of each of the four samples of polywas released under a nitrogen purge and a quantity of (ethylene terephthalate) prepared as described hereinan organic aromatic diisocyanate added to the reaction 40 above and containing various organic aromatic diisocytube. Full vacuum (less than 0.1 millimeter of mercury anate compounds were individually subjected to solid pressure) was then applied to the reaction tube and the state polymerization in the same manner as described temperature of reaction increased to 280 C. The polyin Example 1. Periodic samples were taken during the condensation was continued under these conditions for course of the solid state polymerizations to determine a period of 2 hours, after which the polyester product the increases in l.V. and thus the rate of polymerizawas removed from, the reaction tube, cooled and tion. All pertinent data are listed in the table below. In ground to particles capable of passing a 40 mesh addition, the four samples, after completion of the solid screen. In the single preparation where no diisocyanate state polymerizations, were found to contain 2 eq./ l0

was added the polycondensation, after addition of the g. or less of carboxyl end groups (COOH) as compared antimony trioxide, was carried out in its entirety at 280 to 17 eq./l0 g. of carboxyl end groups for the control C. under full vacuum without 1nterrupt1on. sample (Example 1).

TABLE II Pzn. Sample No.

Time 2(a) 31111 4 (c) 5(0) Min. 1.v. coo 1.v. COOH 1.v. COOH 1v. c0011 1111 Sample contained 0.5 weight percent of dianisidine diisocyanute (bl Sample obtained 0 5 weight percent of bituiylene diisocyunatc 11:) Sample contained 0.3 weight percent of diphenyl methane-4.4'-diisocyana1e (ti) Sample contained 0.4. weight percent of diphenyin1cthanc-4 4-diisocyzmute A comparison of the data in the above Table ll with that in Table I (the control example) discloses that the addition of an organic aromatic diisocyanate greatly reduces thetime required to obtain a high molecular weight polyester product, i.e., a product having an intrinsic viscosity of 1.0 or higher. In other words, the addition of organic aromatic diisocyanate greatly accelerates the polymerization rates for melt polymerized polyester resins subjected to solid state conditions.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What we claim is:

1. In a process for preparing polyester resin having an. intrinsic viscosity of at least 1.0 by solid state polymerization of melt polymerized polyester resin prepared by esterification or transesterification of a dicarboxylic acid or C to C alkyl ester thereof with a glycol of the series HO(CH ),.OH where n is an integer ranging from 2 to and polymerization of the esterification or transesterification product, the improvement which comprises adding to said melt polymerized polyester resin prior to carrying out the solid state polymerization thereof from 0.1 to 2.0 percent by weight of an organic aromatic diisocyanate corresponding to the formula O=C=NRN=C=O where R is a divalent aromatic radical selected from the group consisting of radicals of the formulae r AA tow- 5; 3

where R, is selected from the group consisting of hydrogen atom and alkyl radicals containing from 1 to 10 carbon atoms, R is selected from the group consisting of hydrogen atom, alkyl radicals containing from 1 to 10 carbon atoms and alkoxy radicals containing from l to 10 carbon atoms and Y is selected from the group consisting of a direct bond and methylene radical, said percent by weight of the organic aromatic diisocyanate being based on the weight of the melt polymerized polyester resin.

2. The improvement of claim 1 wherein the melt polymerized polyester resin is poly(ethylene terephthalate).

3. The improvement of claim 1 wherein R of the organic aromatic diisocyanate is a radical of the formula cess for preparing said melt polymerized polyester. 

1. IN A PROCESS FOR PREPARING POLYESTER RESIN HAVING AN INTRINSIC VISCOSITY OF AT LEAST 1.0 BY SOLID STATE POLYMERIZATION OF MELT POLYMERIZED POLYESTER RESIN PREPARED BY ESTERIFICATION OR TRANSESTERIFICATION OF DUCARBOXYLIC ACID OR C1 TO C4 ALKYL ESTER THEREOF WITH A GLYCOL OF THE SERIES HO(CH2)NOH WHERE N IS AN INTEGER RANGING FROM 2 TO 10 AND POLYMERIZATION OF THE ESTERIFICATION OR TRANSESTERIFICATION PRODUCT, THE IMPROVEMENT WHICH COMPRISES ADDING TO SAID MELT POLYMERIZED POLYESTER RESIN PRIOR TO CARRYING OUT THE SOLID STATE POLYMERIZATION THEREOF FROM 0.1 TO 2.0 PERCENT BY WEIGHT OF AN ORGANIC AROMATIC DIISOCYANATE CORRESPONDING TO THE FORMULA O=C=N-R-N= C=O WHERE R IS A DIVALENT AROMATIC RADICAL SELECTED FROM THE GROUP CONSISTING OF RADICALS OF THE FORMULA
 2. The improvement of claim 1 wherein the melt polymerized polyester resin is poly(ethylene terephthalate).
 3. The improvement of claim 1 wherein R of the organic aromatic diisocyanate is a radical of the formula
 4. The improvement of claim 3 wherein the organic aromatic diisocyanate is selected from the group consisting of dianisidine diisocyanate, bitolylene diisocyanate and diphenylmethane-4,4''-diisocyanate.
 5. The improvement of claim 1 wherein the organic aromatic diisocyanate is added to the melt polymerized polyester resin in the polymerization stage of the process for preparing said melt polymerized polyester. 